The present invention relates to a method and apparatus for manufacturing a nonwoven material and, more particularly, to a method and apparatus of manufacturing a nonwoven material using electroejection.
Production of fibrous products is described in various patents inter alia using the technique of electrospinning of liquefied polymer, so that products comprising polymer fibers are obtained. Electrospinning is a method for the manufacture of ultra-thin synthetic fibers, which reduces the number of technological operations and increases the stability of properties of the product being manufactured.
The process of electrospinning creates a fine stream or jet of liquid that upon proper evaporation of a solvent or liquid to solid transition state will yield a nonwoven structure. The fine stream of liquid is produced by pulling a small amount of polymer solution through space by using electrical forces. More particularly, the electrospinning process involves the subjection of a liquefied substance, such as polymer, into an electric field, whereby the liquid is caused to produce fibers that are drawn by electric forces to an electrode, and are, in addition, subjected to a hardening procedure. In the case of liquid which is normally solid at room temperature, the hardening procedure may be mere cooling; however other procedures such as chemical hardening (polymerization) or evaporation of solvent may also be employed. The produced fibers are collected on a suitably located precipitation device and subsequently stripped from it. The sedimentation device is typically shaped in accordance with the desired geometry of the final product, which may be for example tubular, flat or even an arbitrarily shaped product.
Examples of tubular fibrous product which can be manufactured via electrospinning are vascular prosthesis, particularly a synthetic blood vessel, and tubes through which a wire or other device or structure may pass or lie. Tubular fibrous products may also be used as various kinds of artificial ducts, such as, for example, urinary, air or bile duct.
Nonwoven materials manufactured via electrospinning may be shaped in a form appropriate for use as a wound dressing. A particular advantage of the use of electrospun materials is that the fibers may be of very small diameter, to give a mat with small interstices and consequently a high surface area.
Additional examples of end uses for nonwoven products made from electrospun fibers are filtration materials, diaper covers, medical and personal hygiene products, thermal isolation products and clothes having predetermined characteristics, such as biological protection clothes and the like.
In a number of electrospinning applications, particularly in medical implementations, a combination of predetermined strength and elastic properties is required. For example, stent fiber coating should be capable both to expand diameter by hundreds of percents, without strength property degradation, and to preserve an ability for long-term service. Similar problems arise by designing vascular grafts, cardiac valves, and the like. The strength of the nonwoven polymer fiber web depends upon the orientation of the fibers, the mechanical characteristics of the polymer being used, the geometrical size and form of the fibers and the stretching extent of the fibers.
Heretofore, electrospinning has been efficiently used for generating various products. However, conventional nonwoven products exhibit less than optimal cross-directional strength, and less than optimal cross-directional strength in combination with high elongation. The nature of the conventional electrospinning process prevents efficient generation of products having optimal mechanical properties, in particular prior art electrospinning methods cannot be effectively used for manufacturing products having sufficient strength and elasticity.
There is thus a widely recognized need for, and it would be highly advantageous to have, a method of manufacturing a nonwoven material devoid of the above limitations.